The subject matter of the present invention is the recovery of metal values from a complex ore. The recovery comprises an ore pretreatment/leaching sequence.
Complex ores containing large amounts of manganese and lesser amounts of iron, nickel, copper, cobalt, molybdenum and other metals are found as loose deposits in various locations on the ocean floor. These loose deposits are commonly referred to as sea nodules, manganese nodules, ocean nodules, manganese sea nodules, etc. Methods for recovering metals from these nodules are described in U.S. Pat. Nos. 3,723,095, 3,728,105, 3,734,715, South African No. 71/04584, and in U.S. application Ser. No. 396,764, filed Sept. 13, 1973. These methods essentially involve pretreatment of the comminuted ore with gaseous reactant at elevated temperatures, followed by leaching with an aqueous ammonia/ammonium salt solution to extract copper, nickel, cobalt and molybdenum. The only ammonium salts taught to be useful are ammonium carbonate, ammonium halides, e.g., NH.sub.4 CL.sub.4, and ammonium sulfates, e.g., ammonium sulfate.
We have discovered that the amount of cobalt extracted is unexpectedly and substantially increased by introducing sulfite or bisulfite ions into this aqueous leach solution.
Further, we have discovered that pretreatment of the comminuted ore with gaseous reductant prior to leaching can be effected at much lower temperatures than previously reported by the addition of sulfite or bisulfite ions to the leach solution. This represents a substantial economic advantage over known methods of recovering metals from manganese nodules.